Any new item made of cotton has sizing in it, including the fabric from the very best fabric manufacturers. That's how they keep it looking fresh and that's why we're told to wash our fabrics before using, the sizing isn't good for our machines. Once a sheet or any other cotton fabric has been washed, there shouldn't be any problem as long as it hasn't too high a thread count to be easily quilted.
I think a great gift would be a prettily designed sheet set and then a matching flat sheet used for the backing on a quilt to go with it. And if your REALLY liked the person you could buy an extra matching or contrasting flat sheet and make a dust ruffle.